Brief Summary

When an application does not renew the cookie after a successful user authentication, it could be possible to find a session fixation vulnerability and force a user to utilize a cookie known by the attacker. In that case an attacker could steal the user session (session hijacking).

Description of the Issue

Session fixation vulnerabilities occur when:

A web application authenticates a user without first invalidating the existing session ID, thereby continuing to use the session ID already associated with the user.

An attacker is able to force a known session ID on a user so that, once the user authenticates, the attacker has access to the authenticated session.

In the generic exploit of session fixation vulnerabilities, an attacker creates a new session on a web application and records the associated session identifier. The attacker then causes the victim to authenticate against the server using the same session identifier, giving the attacker access to the user's account through the active session.
Furthermore, the issue described above is problematic for sites which issue a session identifier over HTTP and then redirect the user to a HTTPS login form. If the session identifier is not reissued upon authentication, the identifier may be eavesdropped and may be used by an attacker to hijack the session.

Black Box testing and example

Testing for Session Fixation vulnerabilities:
The first step is to make a request to the site to be tested (example www.example.com). If we request the following:

We observe that the application sets a new session identifier JSESSIONID=0000d8eyYq3L0z2fgq10m4v-rt4:-1 for the client.
Next, if we successfully authenticate to the application with the following POST HTTPS:

As no new cookie has been issued upon a successful authentication we know that it is possible to perform session hijacking.
Result Expected:
We can send a valid session identifier to a user (possibly using a social engineering trick), wait for them to authenticate, and subsequently verify that privileges have been assigned to this cookie.

Gray Box testing and example

Talk with developers and understand if they have implemented a session token renew after a user successful authentication.Result Expected:
The application should always first invalidate the existing session ID before authenticating a user and if the authentication is successful, provide another sessionID.